Synthesis And Properties Of Recyclable Polyesters Based On δ-substituted Hexa-cyclic Lactones

Polymer materials are rising with the development of petrochemical industry,which brings great convenience to human society.However,most of these materials are not degradable in the natural environment,and their waste is often treated by centralized landfill or incineration,which inevitably pollute the environment.As people pay more attention to the environment,it is imperative to study new environmentally friendly polymer materials.At present,a major challenge in polymer chemistry is to develop materials that can directly and efficiently recycle monomers or convert waste plastics into high-value chemicals.In this thesis,three six-membered cyclic lactones withδ-substitution of biological source,including:δ-octanolactone（δ-OL）,δ-undecanolactone（δ-UL）andδ-tetradecanolactone（δ-TL）,were studied.In previous reports,ring-opening polymerization ofδ-OL,δ-UL andδ-TL has the problems of long polymerization time and uncontrollable molecular weight.In addition,no reports on the recycling ofδ-OL,δ-UL andδ-TL were found.In this study,an organic base/urea binary catalytic system was used to achieve a rapid and controllable ring-opening polymerization of six-membered cyclic lactones withδ-substitution.Successful preparation of well-defined polymers,including:homopolymerization products of three alkyl-δ-lactones（PδOL,PδUL and PδTL）and triblock copolymers with six-membered cyclic lactones as the soft segment and L-LA as the hard segment（PLLA-b-PδOL-b-PLLA,PLLA-b-PδUL-b-PLLA and PLLA-b-PδTL-b-PLLA）.Experiments show that PδOL,PδUL and PδTL are recyclable polymers,and the LLA in its corresponding triblock polymer can be recovered by alcoholysis,and then PδOL,PδUL and PδTL can be recovered.The specific research content includes the following two parts:（1）The binary catalytic system of t Bu-P₂/urea was used to catalyze the rapid controlled ring-opening polymerization of three biological sources alkyl-δ-lactones（δ-OL,δ-UL andδ-TL）.The polymerization kinetics ofδ-OL,δ-UL andδ-TL were studied,and the apparent rate constants(k_app)were calculated to be 0.29 min^-1,0.31 min^-1and0.30 min^-1,respectively,which were several tens of times higher than those reported in previous literature.The polymerization thermodynamics ofδ-OL,δ-UL andδ-TL were studied,enthalpy changes（ΔH_p^?）were-18.3 k J mol^-1,-17.8 k J mol^-1 and-19.2 k J mol^-1,respectively.The entropy changes（ΔS_p^?）were-60.7 J mol^-1 K^-1,-56.5 J mol^-1 K^-1 and-59.9 J mol^-1 K^-1,respectively.The calculated Gibbs free energy（ΔG_p^?）at 25°C is-0.2k J mol^-1,-1.0 k J mol^-1 and-1.3 k J mol^-1,respectively.Through the polymerization ofδ-OL,δ-UL andδ-TL at different feeding ratios,the experiments show that the open-loop polymerization of the three has good controllability.In addition,the chemical depolymerization of PδOL,PδUL and PδTL resulted in recovery of the original monomers,which were then polymerized again using the recovered monomers to achieve the closed-loop cycle of PδOL,PδUL and PδTL.（2）Based on the studies ofthe preparation of homopolymers PδOL,PδUL and PδTL by ring-opening polymerization ofδ-OL,δ-UL andδTL,the triblock copolymers were synthesized by a one-pot method using a binary catalytic system of t Bu-P₂/diurea.The results of ¹H NMR,¹³C NMR,DOSY and GPC showed that the ABA-type block copolymers with clear structure were prepared.The bonding properties of block copolymer as pressure sensitive adhesive were investigated.The adhesive properties of triblock copolymers were comparable to those of commercial pressure sensitive adhesive without adding adhesive and other additives.After chemical recovery of the three triblock copolymers,the hard segment L-LA was alcoholized into ethyl lactate,which could be used as a green solvent,and the soft segment still had the ability to depolymerize back to monomer after alcoholization of L-LA.